Project Summary/Abstract It is well established that older adults use their ankles less than young adults to propel themselves forward during walking, which has functional consequences like slower preferred walking speed; but the mechanism behind this phenomenon is still not fully understood. In this proposal, the morphology of the Achilles tendon (AT) and plantar fascia (PF) will be investigated as a possible mechanism behind the age-related decline in foot and ankle function. The AT and the PF are anatomically continuous with one another in the very young, potentially allowing for energy transfer across the foot and ankle and aiding in appropriate use of the foot and ankle. However, the AT-PF continuity degrades with age as periosteum formation separates the two at the calcaneus. This age-related degradation of the AT-PF continuity may be a contributing factor in the age-related decline in foot and ankle functioning. The proposed work aims to identify how the AT-PF connection changes across the lifespan, and to use inclined walking as an experimental model and aging as an observational model to determine the role of the AT-PF continuity in foot and ankle biomechanics. The level of AT-PF continuity will be quantified in-vivo with ultrasound. Lower extremity biomechanics will be calculated using a 3D motion capture system and force plates embedded in a treadmill capable of inclining. The AT-PF continuity will then be measured across the adult age span (Aim 1), and we will determine how the AT-PF connectivity affects foot and ankle mechanics during level and incline walking (Aims 2a and 2b). It is hypothesized that the AT-PF continuity will degrade with age, and a degraded AT-PF connectivity will be related to a reduction in ankle moment and power generated during level and inclined walking. The long-term goals of this project are to help understand the mechanisms behind the age-related decline in foot and ankle function and provide a basis for helping the elderly maintain healthy gait biomechanics.